Characterization of optical planar waveguide in Ce:KNSBN crystal formed by triple-energy helium ion implantation

We report on the optical planar waveguide formation and modal characterization in a Ce:KNSBN crystal by triple helium ion implantation at energies of (2.0, 2.2 and 2.4 MeV) and fluences of (1.5, 1.65 and 2.25) × 10¹⁵ cm⁻². The prism-coupling method is used to investigate the dark-line spectroscopy at wavelength of 632.8 and 1539 nm, respectively. The refractive index profiles of the waveguide are reconstructed by an effective refractive index method. It is found that the ion-beam irradiation creates slight increase of extraordinary index whilst decreases ordinary one in the guide region. The modal analysis shows, at wavelength of 632.8 nm, the fields of one TE and three TM modes are well restricted in the guiding region, which means the formation of non-leaky waveguide in the crystal. The damping coefficients of the waveguide are 0.6 and 1.6 cm⁻¹ for ordinary and extraordinary polarized light at 632.8 nm, respectively.     

Defect structure of alumina-rich nonstoichiometric magnesium aluminate spinel

In order to clarify the relation between the dissolution mechanism of hydrogen and the defect structure in alumina-rich nonstoichiometric magnesium aluminate spinels, several compositions of single crystals were grown by the flame fusion method and their compositional dependence of the solubility of hydrogen and that of the mass density were studied by the IR absorption and Archimedes methods, respectively. The solubility of hydrogen increased in proportion to the square root of the water partial pressure and with the increase in the excess amount of alumina. The densities of the single crystals were slightly less than the value calculated based on the reported defect structure. The compositional dependence of the solubility of hydrogen and that of the density can be explained by the model in which the concentration of the oxide ion vacancy increases with the alumina content due to the decrease in the capability of the Mg site to accept the excess Al ion.     

Diffusion of proton in alumina-rich nonstoichiometric magnesium aluminate spinel

The phenomenon of the diffusion of proton and deuteron in a single crystal of magnesium aluminate spinel was studied by infrared absorption. The chemical diffusion coefficient of proton was determined by the relaxation time of the absorption intensity upon the substitution of deuteron with proton. The temperature dependence of the chemical diffusion coefficient of proton for was expressed as . The chemical diffusion coefficient of proton was found to be independent of the composition of spinel and of the atmosphere. Paper presented at the 11th Euro Conference on the Science and Technology of Ionics, Batz-sur-Mer, Sept. 9–15 2007.     

Double optical waveguide in Cu-doped KNSBN crystal formed by MeV boron ion implantation

We reported for what is to be believed the first time a double optical waveguide in a Cu-doped potassium sodium strontium barium niobate (KNSBN) crystal formed by double boron ion implantation. The energy and dose of B⁺ and B³⁺ ions were (3+6) MeV and (2+2)×10¹⁴ ions/cm², respectively. The refractive index profile of the waveguide showed a double-barrier confined shape, which suggested the formation of a two-layer waveguide structure. The two waveguide layers were with thickness of 2.6 and 2 μm, respectively, which was in a good agreement with the parameters obtained from transport and range of ions in matter 98 (TRIM) code simulation. The nuclear energy loss distribution of the MeV B ions implanted into this crystal had a similar shape to that of the waveguide index profile, which means an inherent relationship between the waveguide formation and the energetic energy deposition.     

Optical waveguide in Nd:Bi_(12)SiO_(20) crystal produced by multi-energy C ion implantation

We report the fabrication of a planar waveguide in the Nd:Bi_(12)SiO_(20) crystal by multi-energy C ions at room temperature. The waveguide is annealed at 200℃, 260℃, and 300℃ in succession each for 30 min in an open oven. The effective refractive index profiles at transverse electric(TE) polarization are stable after the annealing treatments. Damage distribution for multi-energy C ion implanted in Nd:Bi_(12)SiO_(20) crystal is calculated by SRIM 2010. The Raman and fluorescence spectra of the Nd:Bi_(12)SiO_(20) crystal are collected by an excitation beam at 633 nm and 473 nm, respectively. The results indicate the stabilization of the optical waveguide in Nd:Bi_(12)SiO_(20) crystal.     

Modification of silicon waveguide structures using ion implantation induced defects

The structure of re-crystallized silicon films is investigated using transmission electron microscopy, spectroscopic ellipsometry and positron annihilation spectroscopy. Samples were prepared via amorphization of the silicon overlayer of silicon-on-insulator substrates, and subsequent thermal annealing. For an annealing temperature of 650 °C we show that the silicon film has a poly-crystalline structure. Its refractive index measured at 1550 nm is comparable to that of crystalline silicon following re-crystallization at 750 °C. Positron measurements indicate a high concentration of open-volume point defects in the re-crystallized films. We discuss the potential importance of these structures with regard to defect engineering for silicon photonic devices.     

Defects and radiation induced electronic processes in magnesium aluminate spinel of different compositions

The time dependence of the formation and decay of irradiation-induced optical absorption centers in magnesium aluminate spinel single crystals of different compositions (MgO - 1.0Al 2 O 3 and MgO - 2.5Al 2 O 3 ) was investigated. The kinetics of accumulation of X-ray irradiation-induced absorption bands is consistent with the mechanism of trap filling with free charge carriers through the conduction band. The model includes Coulomb blocking effects on spatially correlated defects. The observed two-stage decay of absorption bands after termination of X-ray irradiation is explained by electron hole recombination between centers of two different distances and/or different potential barriers. UV-irradiation confirms the existence of charge exchange between complex spatially correlated defects.     

Vibrational and dielectric properties of magnesium aluminate spinel: A first-principles study

The vibrational and dielectric properties of MgAl₂O₄ are investigated within the framework of density functional perturbation theory. Results of phonon frequencies at the Brillouin zone center, static dielectric constant, and electronic dielectric constant are reported. In comparison with experimental results, we find that the generalized gradient approximation potential results in more accurate phonon frequencies than local density approximation potential does. Dielectric, refractive index, extinction coefficient and infrared reflectance spectra of MgAl₂O₄ are given, and the figures suggest that MgAl₂O₄ presents good transmission properties in the spectrum range above 1000 cm−1 and below 300 cm−1.     

Fabrication of waveguides in Yb:YCOB crystal by MeV oxygen ion implantation

Oxygen ions with energies of 6.0 or 3.0 MeV were implanted into y-cut Yb:YCOB crystals at fluences ranging from 5.0 × 10¹³ to 2.0 × 10¹⁵ ions/cm² at room temperature, forming optical planar waveguide structures. Dark-mode line spectroscopy was applied at two wavelengths, 633 and 1539 nm, in various excitation configurations, showing strong enhancement of one of the indices (n_x) in the implanted near surface. The n_x refractive index profile is reconstructed by a reflectivity calculation method and compared to the ion energy losses profiles deduced from SRIM-code simulation. Moreover, the near-field patterns were imaged by an end-fire coupling arrangement.     

Optical terahertz wave generation in a planar GaAs waveguide

We report generation of terahertz (THz) radiation in a planar 61-microm-thick GaAs waveguide with a TM0 propagation mode, achieved by phase-matched difference frequency mixing. The THz output was centered near 2 THz and had 1 microW average power. As a pump source we utilized both the signal and the idler outputs of a near-degenerate type II synchronously pumped optical parametric oscillator operating near 2 microm with the average powers of 250 and 750 mW, correspondingly.     

Annealing effect on planar waveguides in LiNbO3 produced by oxygen ion implantation

We reported on planar waveguides in stoichiometric lithium niobate fabricated by 4.5 MeV oxygen ion implantation with a dose of 6 × 10¹⁴ ions/cm² at room temperature. After ion implantation, these samples were annealed at 240 °C, 260 °C, and 300 °C for 30 min. We investigated annealing effect on the guiding modes and near-field images in the waveguides by prism-coupling method and end-face coupling method respectively. We found that for the extraordinary refractive index a positive alternation occurred in the near-surface region while a negative alternation happened at the end of ion track. Moreover, we measured the transmission spectra for the pure sample and implanted samples before and after annealed at different temperatures, and we observed an absorption peak at ∼480 nm (2.6 eV) in all of these SLN samples.     

Characterization of optical waveguide in Nd: GdVO4 by triple-energy oxygen ion implantation

We report on the optical planar waveguide formation and modal characterization in Nd: GdVO₄ crystals by triple oxygen ion implantation at energies of (2.4, 3.0, and 3.6 MeV) and fluences of (1.4, 1.4, and 3.1)  × 10¹⁴ions/cm². The prism-coupling method is used to investigate the dark-mode property at wavelength of 632.8 nm. The refractive index profiles of the waveguide are reconstructed by an effective refractive index, n_eff method. The modal analysis shows that the fields of TE modes are well restricted in the guiding region, which means the formation of nonleaky waveguide in the crystal.     

Optical waveguide with homogeneous refractive index profile in LiNbO3 by double-low-energy Oxygen ion implantation

We report on the formation of the planar waveguide by 550 keV O ion followed by 250 keV O ion implantation in lithium niobate (LiNbO₃), at fluences of 6 × 10¹⁴ ions/cm² and 3 × 10¹⁴ ions/cm², respectively. The Rutherford backscattering/channeling spectra have shown the atomic displacements in the damage region before and after annealing. A broad and nearly homogeneous damage layer has been formed by double-energy ion implantation after annealing. Both the dark mode spectra and the data of refractive index profile verified that the extraordinary refractive index was enhanced in the ion implanted region of LiNbO₃. A homogeneous near-field intensity profile was obtained by double-low-energy ion implantation. There is a reasonable agreement between the simulated modal intensity profile and the experimental data. The estimated propagation loss is about 0.5 dB/cm.     

Characterization of optical waveguide in Nd: LuVO4 crystals by triple-energy oxygen ion implantation

We report on the optical planar waveguide formation and modal characterization in Nd:LuVO₄ crystals by triple-energy O³⁺-ion implantation at energies of 2.4, 3.0, and 3.6 MeV and doses of 1.4, 1.4, and 3.1×10¹⁴ ions/cm², respectively. The prism-coupling method is used to investigate the dark-mode property at a wavelength of 633 nm. The refractive index profiles of the waveguide are reconstructed by the reflectivity calculation method (RCM). The modal analysis shows that the fields of TE modes are well restricted in the guiding region, which indicates the formation of non-leaky waveguide in the crystal.     

Optical confinement of spatial frequencies in the photonic crystal waveguide

The optical confinement of spatial frequencies in the photonic crystal waveguide has been investigated theoretically and simulated numerically. It is found that the enhanced gap confinement is at frequency close to the upper band edge, in contrary to the conventional concept that the strongest optical confinement is found at frequencies near the mid-gap. The anomalous phenomenon may be attributed to a Van Hove saddle point singularity in a band adjacent to a photonic crystal band gap. In general, the saddle point favors the appearance of a very flat band, which in turn causes an enhanced confinement at band-gap frequencies.     

Stress reduction in planar waveguide using polymer top layer

Planar optical waveguides consisting of layers from different materials created at elevated temperatures usually exhibit substantial stresses. By controlling the layer thickness of polymeric top layer on planar waveguide structures, it is possible to use very thin layers for stress compensation, significantly reducing required deposition times. It is possible to reduce birefringence within planar device by controlling top polymer layer thickness with thermal expansion coefficient greater than silica or PMMA.     

Lithium niobate planar and ridge waveguides fabricated by 3 MeV oxygen ion implantation and precise diamond dicing

We report on the fabrication and optimization of lithium niobate planar and ridge waveguides at the wavelength of 633 nm.To obtain a planar waveguide, oxygen ions with an energy of 3.0 Me V and a fluence of 1.5 × 10~(15) ions=cm~2 are implanted in the polished face of Li Nb O_3 crystals. For planar waveguides, a loss of 0.5 d B/cm is obtained after annealing at 300°C for30 min. The ridge waveguide is fabricated by the diamond blade dicing method on optimized planar waveguides. The guiding properties are investigated by prism coupling and end-face coupling methods.     

Ti:sapphire rib channel waveguide fabricated by reactive ion etching of a planar waveguide

We report, to our knowledge, the first active channel waveguide in Ti:sapphire. We have created ∼1.4-μm high ribs in a ∼10-μm thick Ti:sapphire planar waveguide by reactive ion etching. Following excitation by an Ar-ion laser, the rib structure showed channel-waveguide fluorescence emission. The mode profiles and the beam-parameter values (M²) were measured. The coupling efficiency of fluorescence emission into a single-mode fiber was an order of magnitude higher than for fluorescence from unstructured planar regions of the waveguide. Such devices are of interest as low-threshold tunable lasers and as broadband light sources in low-coherence interferometry. Received: 22 December 2002 / Revised version: 30 March 2002 / Published online: 8 August 2002     

Optical pulse compression of ultrashort laser pulses in an argon-filled planar waveguide

We investigate the possibility of optical pulse compression of high energy ultrashort laser pulses in an argon-filled planar waveguide, based on two level coupled mode theory and the full 3D nonlinear Schr?dinger equation. We derive general expressions for controlling the spatial beam profile and the extent of the spectral broadening. The analysis and simulations suggest that the proposed method should be appropriate for optical pulse compression of ultrashort laser pulses with energies as high as 600 mJ.